Ultra high frequency transceiver



Feb. 14, 1939. D, .1 HILFERTY 2,147,595

` y ULTRA HIGH FREQUENCY TRANSCEIVER .Filed Deo. 9, 1937 :inventor i or loudspeaker.

UNITED STATES PATENT OFFICE ULTRA HIGH FREQUENCY TRANSCEIVER Daniel J. Hilferty, Merchantville, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application December 9, 1937, Serial No. 178,84*?

Claims.

My invention relates to radio receivers and more particularly to a'receiver of the superref generative type in which the inherent noise volt*- age is used to bias the detector when no radio frequency signal is reecived. l

It is well known to those familiar with the com ventional superregenerative receiver that when no signal is received the receiver generates a most annoying noise or hash in the headphones This noise disappears Awhen a signal carrier is received, probably because of the biasingaction of the signal on the detector tube.

I am awareof various automatic volume con- .15 trolsysterns which operate on the sensitivity of a receiver in proportion to the intensity of the `radio frequencycarrier. I am also awareof in- -fterstation noise suppressor` systems Whichpermit .the receiver to be'receptivevonly when a radio ..20 .frequency Isignal -is impressed on the `control .,fcircuit.

In mylnvention `I proposeto utilize the noise voltage `or hashy whichis `present `in the audio ,circuit to provide,lafter rectification, a negative 25 d.c. biasing `voltage -which may then be applied 5to the gridiof .the detector tube to-decrease this objectionable noise. When ya radio frequency `signal -is received 'the noise is Lthereby reduced, ithus the noise-.controlledbias is reduced, and the 30 .receiver wi-ll `operate normally.

An especially valuable feature is obtained .when my invention is used with a communication system -as shown in Fig. 2. When the switch is `in the transmit position the device becomes a 35 "transmitter and may be used to send out voicemodulated signals. By operating the switch the system is converted into a receiver, so -that rapid -tWo-Way communication may be carried on. It `will be noted that, if the switch is thrown to the '40 receive position before the carrier signal from the `transmit-,ter with which communication is being held has been turned on, a conventional receiver would set up a very loud and objection- 45 able noise, which is especially unpleasant if the operator is using headphones in connection with the receiver. However, if the system disclosed in my invention is used in connection with such a transmitter-receiver, the operator will never 50 have to suffer the inconvenience of this noise,

` and conversation can be carried on with a minimum of effort.

One of my objects is therefore to provide means `whereby the noise voltage in a superregenerative 55 receiver may be used to limit the sensitivity of (Cl. Z50-Z0) the receiver during the time in which no signal is received.` Y v c Y c It is another object of my invention to provide a means whereby a d. c. biasing or control voltage may be obtained from the noise or hash voltage present in a superregenerative receiver.

It is another object of my invention to provide a means of limiting the noise or hash voltage which is present in conventional superregenerative receivers.

It is another object of my invention to provide means for interstation noise suppression in la superregenerative receiver.

It is another object of my invention to provide means for more effective two-way communication betweentwo or more transmitter-receivers by preventing a sudden surge of-noise in any receiver should` the switch be placed in the receive position at a `time when no `signal is being received. c

My invention will be better understood from the following description when considered in connection with the accompanying drawing. Its scope is indicated by the appended claims.

Referring to the drawing,

Figure 1 is a circuit diagram of an embodiment of my invention wherein the noise reducing device is applied to a superregenerative receiver; and

Figure 2 is a circuit diagram of another em- 30 bodiment of my invention wherein the noise reducing device is applied to a system which may be used either for reception` or transmission.

Referring especially to Fig. 1, an antenna I, which may be of any well-known form, is coupled through a capacitor 3 to a tap on an inductor 5. The inductor 5, together with the variable capacitor l which is shunted across it, forms the resonant circuit of the familiar ultra audion oscillator. One end ci the resonant circuit -5 and l is coupled through a grid capacitor 9 to the grid of a diode-triode type vacuum tube ll the other end of the resonant circuit is connected to the anode of tube H. This anode is connected through a radio frequency choke coil 4.5 I3 to one terminal of the primary of an audio frequency transformer I5; the other terminal of the primary is connected to a suitable source of d.c. potential, which may be derived from a conventional rectifier and lter source or may be derived from a battery 3|, as shown in the diagram.

The cathode of tube Il, as well as one of the heater terminals, is grounded. The other terminal oi the heater, as well as the heater of the audio amplifier tube 23 later to be described, is connected through the switch 5| to a suitable battery 45. The said heaters may be energized by a suitable a.c. source in a manner well known to those skilled in the art. The anode battery 3I is by-passed by a capacitor 4|. The grid of tube II is connected to ground through two resistors in series; the first, I1, is a grid leak resistor; the second, I9, is a diode load resistor. The midpoint of the resistors I1 and I9 is connected to the low potential terminal of the secondary winding of the audio frequency transformer I5. The diode load resistor I9 is shunted by an audio frequency bypass condenser 2|. The remaining terminal of the secondary winding of transformer I5 is connected to the two diode electrodes in tube II, and to the grid electrode of the audio frequency amplifier tube 23.

The amplifier tube 23 preferably includes a self-biasing resistor 25, bypassed by a capacitor 21, connected in the cathode circuit in the conventional manner. While headphone receivers 29 are shown in the output circuit of the amplifier tube, it is, of course, understood that the headphones may be replaced by a loudspeaker, or an audio frequency amplifier. The screen grid electrode of the amplifier tube 23 and the low potential side of the headphones 29 are connected to the positive high potential terminal of battery 3l.

The operation of the circuit is understood to be as follows:

The cathode, grid and plate electrodes of the vacuum tube II, together with the resonant circuit 5 and 1, grid capacitor 9, and grid leak I1, constitute an oscillator circuit which will generate oscillatory currents at a frequency determined by the resonant frequency o f inductor 5 and capacitor 1. While I prefer this particular oscillatory circuit, my invention is not limited to it, as any other equivalent circuit may be employed. When the grid capacitor 9 and the grid leak resistor I1A are properly chosen, the tube does not generate steady oscillatory currents, but the oscillatory currents are interrupted at a frequency which is determined by the time constant of the grid capacitor 9 and the grid leak I1. By way of example, the capacitor 9 may have a capacity of 50 micromicrofarads and the resistor I 1 a resistance of 0.1 megohm. These values provide an interruption frequency which is superaudible; i. e., of the order of ten to twenty thousand cycles per second.

The interruption of oscillatory currents at the so-called "interruption or quenc frequency causes superregenerative action to take place in the tube II. When a signal from the antenna is impressed on the grid of tube I I, demodulation is effected and an audio frequency component appears across the primary of transformer I5. The radio frequency choke I3 is an inductor which presents a Very high impedance to radio frequency currents, but which will readily pass audio frequency variations of the plate current, and thus serves to isolate the transformer I5 from the radio frequency circuits. This method of operation is well known to those skilled in the art.

My invention relates more particularly to features now to be discussed. Any voltage appearing across the secondary of transformer I5 is applied to the audio frequency amplifier tube 23, and to the diodes and the cathode of tube II through the diode load resistor I9 and capacitor 2|. Thus the noise-representing voltage,

which appears across the secondary of transformer I5, is rectified by the diode-cathode operation, and a d.c. current ows through the diode load resistor I9 in such direction as to make the ungrounded terminal of said resistor I9 become negative with respect to ground. The audio frequency bypass condenser 2| shunted across resistor I9 provides a low impedance path for the noise voltage, so that the full voltage appearing on the secondary of transformer I5 is impressed across the diode-cathode rectifier elements of tube II. Since the grid electrode of tube I I is connected to the ungrounded terminal of resistor I9, the grid also becomes negative with respect to ground, thus effectively cutting down the noise voltage without materially reducing the sensitivity of the detector tube II. When a signal carrier voltage appears across the resonant circuit 5 and 1 and is impressed on the grid of tube II, the grid is made more negative and the noise is reduced or eliminated by operation of the signal, so that there is no noise voltage to be rectified by the diodes when a signal is received. A further feature of my invention is that during periods in which the noise voltage has been reduced by the incoming signal voltage, the audio modulation component which appears across the secondary of transformer I5 also appears across the diodes, and is rectified to provide a bias voltage which tends to hold the audio output at a constant level regardless of variations in modulation percentage in the incoming signal.

Referring now to Fig. 2, a second application of my invention is shown. When the transmitreceive switch 49 is in the receive position, the circuit and operation is seen to be identical with that just described for Fig. 1. However, when the switch 49 is in the transmit position, the circuit is changed to that of a conventional ultrahigh frequency transmitter. A microphone transformer 31 is added having one terminal of its primary connected through a microphone 39 and the switch 5I to a suitable source of d.-c. potential, and the other terminal grounded. For convenience, I have shown the battery supplying the energy for the heaters of tubes II and 23 as Well as for the microphone, but it will be realized that a separate microphone battery will be required if the heaters are energized from an a.c. source. The grid electrode of tube 23 is connected through the secondary winding of transformer 31 to ground. The switch 49 also connects the plate of tube 23 to the junction of the primary winding of transformer I5 and the choke coil I3. A resistor 53 is inserted between the plate of tube 23 and the headphones, whereby the transmitted signals may be heard by the operator. Switch 49 also connects a resistor 33 between the grid of tube II and ground.

When the switch 49 is placed in the transmit position, the transmitter operates in the conventional manner. Resistor 33 changes the operating grid potential of the oscillator tube II to such a point that smooth continuous oscillation takes place. To accomplish this, resistor 33 preferably has a resistance of the order of 40,000 ohms. The microphone 39 is responsive to sound waves, and will impress an audio frequency voltage on the grid of the tube 23 through transformer 31. Since tubes I I and 23 have as a common impedance in their plate circuits the primary of transformer I5, modulation of the radio frequency output of tube II takes place, as is well known. Since the grid of tube II is conu nected to ground through resistor 33, it is obvious that the negative voltage appearing across resistor I9 has no effect during periods of transmission, but immediately upon placing the switch 49 in the receive position, the noise Will be reduced as shown above.

I claim as my invention:

1. A superregenerative radio receiving system comprising means for receiving currents yof carrier frequency, means for generating currents of quenching frequency, means for applying said currents of quenching frequency to said firstnamed means, means for rectifying transient currents representing noise established by said quenching frequency currents, means for obtaining a biasing voltage from said rectified currents, and means for applying said biasing voltage to said first-named means.

2. In a radio receiver of the superregenerative type, means for receiving signals of carrier frequency, means for demodulating said signals of carrier frequency, means for obtaining currents of quenching frequency, said quenching frequency being lower than said carrier frequency, means for applying said quenching currents to said demodulating means, means for rectifying transient currents representing noise created by said quenching currents, means for obtaining a biasing voltage from said rectied currents, and means for applying said biasing voltage to said demodulating means. v

3. In a radio receiver of the superregenerative type, means for receiving signal currents of a desired carrier frequency, means for demodulating said signal currents including a thermionic vacuum tube oscillating at the frequency of said carrier frequency, means for interrupting said carrier frequency oscillations at a frequency substantially lower than said carrier frequency, means for rectifying transient currents representing noise created by said interruptions, means for obtaining a biasing Voltage from said rectified currents, and means for applying said biasing voltage to said demodulating means.

4. In a superregenerative radio receiver, the method of controlling undesired noise-representing currents generated by the quenching operation, which includes resonating currents of carrier frequency, applying said resonated currents to local oscillatory currents having the same frequency as said carrier currents, interrupting said local oscillatory currents at quenching frequency, said quenching frequency being substantially lower than said carrier current frequency, demodulating said carrier currents, rectifying the noise-representing currents established by said interruption, and applying said rectified currents to reduce the intensity of said noise-representing currents.

5. In a superregenerative radio receiver, the method of controlling undesired noise-representing currents, generated by the quenching operation, which includes rectifying said noise-representing currents, and applying said rectified currents to reduce the intensity of said noise-representing currents.

DANIEL J. HILFER'I'Y. 

